Mobile communication devices, such as cellular telephones can include speakerphones. The requirement for full-duplex communication in handsfree mode is fairly recent. Handsfree mode refers to the ability to carry on communication without the need to hold the mobile communication device in one's hand, for example, by use of a car kit or a mobile communication device equipped with a speakerphone. In full-duplex communication the transmission of data occurs in two directions simultaneously. A wireline telephone is a full-duplex device because both parties can talk at once. In contrast a walkie-talkie is a half-duplex device because only one party can transmit at a time. Until the requirement for full-duplex communication was made in mobile communication devices, and in particular cellular telephones, echo algorithms were capable of handling the inherent feedback between the speaker and the microphone in a mobile communication device that is not a full-duplex device.
A difficulty with full-duplex communication in handsfree mode is that the microphone is expected to pickup and transmit what the user is saying while at the same time the loudspeaker or speakerphone speaker is presenting speech. The signals from the speakerphone speaker can travel through air and can be picked up by the microphone as it transmits signals. Therefore when a speakerphone speaker and a microphone are within close proximity or are in the same housing, substantially perfect sealing and/or echo algorithms may not sufficiently reduce echo.